It is not required. Some people argue that it does not help, but it will not hurt you to send one anyways. People typically send these when they are waitlisted or have not heard anything from the schools in a while.
I sent a letter of intent to GA-PCOM after my last interview. I had interviewed with GA-PCOM about a week before, and the letter basically said that I had seen everything I needed to see, and that I was ready to make a decision, and that they are my top choice. Little did I know that an acceptance letter from them was already in my mailbox when I sent it, so I can't say if it would have mattered or not. However, people in admissions from LECOM-B and DMU have told me that it could make a difference. Of course, they cannot speak for other schools.